The present invention relates to impeller type propulsion systems, and more particularly, to a propeller system adapted for precision control of a submersible vehicle in six different degrees of freedom.
There are many uses for an unmanned (remotely piloted) deep submersible ocean vehicle such as maintenance and repair of underwater oil well facilities, location and recovery of sunken aircraft and underwater surveying. Commands and sensor data from cameras and other on-board instrumentation may be transmitted to and from the vehicle via a tether or sonar. Such a deep submersible vehicle must be capable of a high degree of maneuverability and precision control in a reliable manner in order to effectively accomplish such tasks. In particular, such a submersible vehicle must be able to make precise translational and rotational movements relative to the surge (fore-aft), sway (athwartship), and heave (vertical) axes. Such a vehicle must also be capable of maintaining any attitude to perform its tasks, and it must be able to exert large forces and moments with precision.
Heretofore remotely piloted deep submersible vehicles for performing this type of work have typically included a frame or sled with a viewing camera, lights, robot arms and a plurality of outboard thrusters for movement relative to the three different axes. These thrusters have typically been hydraulic and have required complex control mechanisms. The efficiency and response time of such thrusters and their ability to accomplish precision maneuvers are limited.
In U.S. Pat. No. 3,101,066 of Haselton there is disclosed a submarine with fore and aft counter-rotating propellers, and mechanisms for controlling the cyclical and collective pitch of the blades of each of the propellers independently for maneuvering the vehicle in six degrees of freedom. Mechanisms which have heretofore existed for accomplishing cyclic and collective pitch control have typically been complex mechanical arrangements similar to the swash plate mechanisms in helicopters. Such mechanisms require a great deal of maintenance and are therefore unsuitable for submarine use. In addition, they can only change blade pitch sinusoidally, i.e. the blade angle alpha varies as a sinusoidal function of the angular position theta of the blade relative to the rotational axis of the propeller, owing to the geometry involved in a swash plate mechanism. This imposes a limitation on the ability to achieve precise maneuvers.